Dave's   DGen   Emulator
it's all just another bit of history repeating...
Download DGen here:
DGen v1.21 for Windows (read what's new in dgen.txt).

DGen is a free Genesis/Megadrive emulator for Windows 95/98/2000 (and possibly NT) running under DirectX. It has sound. Recommended computer is a Pentium-II.

July, 27th 2021:
Some interesting news from CPS2Shock. They can now decrypt any memory location! Nice one guys!
It sounds like it takes time to decrypt each address, so obviously there's still some work to be done... but it's a major breakthrough.

May, 30th 2020:
I just wanted to publicise this a little bit here, because it captured my imagination. It's the work on the Capcom CPS-2 series (Super Street Fighter 1/2, SF Alpha 1/2/3, X-Men Children of the Atom etc.). There is no emulator for these games and I am not working on one, but as I understand is these titles would be very straightforward to emulate, if it wasn't for a custom cpu with encryption on the 68000 code. Also, these arcade boards commit suicide (I kid you not!) in their physical form after a few years.
Feel like a bit of code-breaking? Here's an example from the CPS2Shock team:

            3D7C 00F0 0014   MOVE #$00F0,20(A6)
Encrypted : 0151 4E08 DF0A

            3D7C 0030 0014   MOVE #$0030,20(A6)
Encrypted : 0151 3F01 DF0A
But here's the large catch: In true Enigma-machine style, an opcode translates to a different code in a different place.
Here's the site, with loads more stuff including a section of code which is known to be a long sequence of zeros - these guys are brilliant so have a look at the work they have been doing: https://www.cps2shock.retrogames.com/

April, 21th 2019:
Lot of people have been asking, so here's a link to the site which explains how to reproduce on a Genesis emulator the "Lock-On" (cart combination) feature found in the Sonic series:
Lock-On Guide

March, 19th 2019:
Here's some information about joypads: I thought I had uploaded this paragraph months ago, but I guess I must have forgotten...
A Frequently Asked Question is how to get PC joypads/sticks working:
It seems some of you haven't installed them under Windows correctly, so either refer to the joypad's manual, or follow these instructions:
First make sure DGen isn't running and go to the windows control panel.
Select Game Controllers and click Add. Select the joypad which best matches yours (don't worry too much about this).
Now highlight it, click Properties, the Settings tab, and then Calibrate. Follow onscreen instructions - calibration is important.
Now play a game which uses DirectInput (e.g. Tomb Raider III) and check that your joypad correctly controls the game - if it doesn't, contact your joypad supplier.
If you are sure you are able to play a DirectX game with your joypad, load up DGen and select the second option from the Input Menu.
DGen should now work with your joypad. If the buttons are mixed up, use the redefine keys option from the Input menu to fix this.

Guides

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Dave's Genesis Tests

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Take notice of this before sending me any mail:

  1. The text on Shining Force can be fixed by switching to Musashi 68000 emu.
  2. I know Shinobi 3/Warsong/Phantasy Star 4 are broke.
  3. No ROM requests.
  4. If it's about the Mac version, don't ask me (click on the below Mac/OS link).
  5. Ask before sending files bigger than 100k.
  6. I will not be adding Sega CD, 32X, or Virtua Racing support to DGen.
  7. DGen needs a fast computer to run (P2-333-ish).
  8. I know about the fullscreen menu glitches.
  9. I know that interpolation/higher resolution/scanlines would be nice.

Ports to other systems
DGen/MacOS | DGen/Linux | DGen/BeOS

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(Archive)
DGen-DOS v1.04A - dgend104.zip (no sound)
Here is the v1.17 source dgens117.zip.
v1.15 source: dgens115.zip v1.09 source: dgens109.zip v1.03 source: dgens103.zip
Binaries: dgen1181.zip, dgen117.zip, dgen115.zip, dgen114.zip, dgen112.zip, dgen111.zip, dgen110.zip, dgen109.zip, dgen108.zip, dgen107.zip, dgen105.zip, dgen104.zip, dgen103.zip, dgen101.zip, dgen10b.zip.

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The very very old DTMNT page is here